title: Chronotype as modulator of morning serum melatonin levels.
abstract: BACKGROUND
  The search for biological markers of individual characteristics has produced scanty results. Melatonin (MLT), the main hormonal product of the pineal gland, has been used as a biological marker of neuroticism, introversion-extroversion and morningness-eveningness. Morningness-eveningness indicates preferences associated with morning or evening activities. The goal of this research is to study if serum MLT levels are related to morningness-eveningness preference.
  
  
  METHODS
  Twenty-three morning type and twenty-one evening type healthy volunteers took part in the study. Morningness-eveningness was evaluated with the Composite Scale of Morningness. Blood was drawn at 09:00, 12:00 and 00:00 h. MLT levels were measured with an ELISA.
  
  
  RESULTS
  At 09:00 h evening type subjects had significantly higher serum MLT levels than morning type subjects (8.4±3.6 pg./ml. vs. 4.6±3.2 pg./ml., p<0.02).
  
  
  CONCLUSIONS
  Morning serum MLT may be used as a biological peripheral marker of morningness-eveningness preference. Our results emphasise the convenience of expanding MLT studies until 09:00 h when differences between morning type and evening type subjects may still be found.
authors.affiliation: Departamento de Medicina Interna, Dermatología y Psiquiatría Facultad de Medicina. Universidad de La Laguna Tenerife. España Consultoría Psiquiátrica SC Santa Cruz de Tenerife. España.
authors.forename: Armando L
authors.initials: AL
authors.lastname: Morera-Fumero
authors.forename: Pedro
authors.initials: P
authors.lastname: Abreu-González
authors.forename: Manuel
authors.initials: M
authors.lastname: Henry-Benítez
authors.forename: Estefanía
authors.initials: E
authors.lastname: Díaz-Mesa
authors.forename: Silvia
authors.initials: S
authors.lastname: Yelmo-Cruz
authors.forename: Ramón
authors.initials: R
authors.lastname: Gracia-Marco
mesh_terms: D000328:Adult; D057906:Circadian Clocks / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008550:Melatonin / Q000097:blood*
chemical_list: D008550:Melatonin